1. Field of the Invention
This invention relates to a thickener to be contained in a coating material for forming a vibration damper and more particularly to a thickener which is capable of enhancing the drying property of a coating film and repressing the occurrence of a crack and an expansion of the surface of the coating film.
2. Description of the Related Art
The coating material is expected to possess various qualities to suit purposes such as protection, insulation, and beautification. The vibration damper is one of the uses found for the coating material. The term “vibration damper” refers to a material which is disposed on the surface of a material for the purpose of blocking transmission of sound and preventing vibration. The vibration damper is preferred to be disposed on the surface of the chassis of an automobile, for example, with the object of keeping the interior of the automobile quiet.
The sound insulating sheet may be cited as the material which can be utilized as-the vibration damper. The disposal of the sound insulating sheet, however, consumes labor hour. Particularly when this disposal is effected on such a member as the chassis of an automobile which possesses a complicated surface contour, marked decline of productivity cannot be avoided. It is not easily automated and this fact obstructs efforts to cut the cost of production.
The coating film which possesses the quality of a vibration damper, therefore, has been attracting attention. The technique concerning the coating film which functions as a vibration damper has been embodied, for example, by copolymer latex for vibration damper obtained by emulsion polymerizing a monomer mixture comprising a conjugate diene type monomer (a), an ethylenically unsaturated monomer possessing an epoxy group (b), an ethylenically unsaturated carboxylic acid amide monomer (c), and an ethylenically unsaturated monomer (d) other than (b) and (c) at a specific weight ratio (see, the official gazette of JP-2000-178499). The vibration damper is formed by using the coating material incorporating the latex therein. The formation of the vibration damper which is attained by using such a coating material as this excels in productivity and permits automation.
To function effectively as the vibration damper, the coating film is required to:possess a uniform wall thickness. Incidentally, when a thick coating film is to be dried, since it tends to dry gradually from the first surface onward, the part of the coating film in the proximity of the first surface is completely hardened while the inner part of the coating film still retains water. Thus, the vaporization of the water inside the coating film poses the problem of suffering the part of the coating film already hardened in the proximity of the first surface to expand outward and the problem of causing the coating film to sustain a crack. When the coating film expands or cracks, the quality thereof as the vibration damper will be greatly degraded. This mishap deprives the elaborate formation of the coating material with the object of being utilized as the vibration damper of its significance. These problems gain particularly in prominence when the coating film is formed by using an emulsion coating material. The reason for this prominence is that the emulsion coating material tends to succumb to fusion quickly and form a film when the water content encompassing particles is decreased.